<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="f(1)">
<input type="button" value="减" onclick="f(2)">
<input type="button" value="乘" onclick="f(3)">
<input type="button" value="除" onclick="f(4)">
<div>
    结果: <span></span>
</div>

<script>
    function f(x) {
        //获取两个文本框  给元素添加id  浏览器会自动生成代码
        // let i1=document.getElementById("i1")
        // let i2=document.getElementById("i2")
        let span = document.querySelector("span")
        switch (x) {
            case 1:
                span.innerText = i1.value * 1 + i2.value * 1
                break
            case 2:
                span.innerText = i1.value - i2.value
                break
            case 3:
                span.innerText = i1.value * i2.value;
                break
            case 4:
                span.innerText = i1.value / i2.value;
                break
        }

    }


    function f1() {
        let i1 = document.getElementById("i1")
        let i2 = document.querySelector("#i2")
        let s = document.querySelector("span")
        s.innerText = parseFloat(i1.value) + parseFloat(i2.value)
    }

    function f2() {
        let i1 = document.querySelector("#i1");
        let i2 = document.querySelector("#i2");
        let s = document.querySelector("span");
        s.innerText = i1.value - i2.value;
    }

    function f3() {
        let i1 = document.querySelector("#i1");
        let i2 = document.querySelector("#i2");
        let s = document.querySelector("span");
        s.innerText = i1.value * i2.value;
    }

    function f4() {
        let i1 = document.querySelector("#i1");
        let i2 = document.querySelector("#i2");
        let s = document.querySelector("span");
        s.innerText = i1.value / i2.value;
    }


</script>

</body>
</html>